Commercial concrete is a mixture of cement, sand, and stone aggregate that, after the addition of water, slowly hardens together into a rigid structure. Stresses within concrete structures are typically of three primary types: compressive (where particles are crushed together), tensile (where particles are pulled apart), and shear (where one section of a structure is pressured to slide upon an adjacent section).
Unreinforced concrete structures often have good resistance to compressive stresses. However, any significant tensile stresses tend to cause undesirable cracking and separation since concrete is relatively weak in tension. To address this problem, concrete structures are typically reinforced by embedding smaller solid members made of material(s) with high strength in tension. Typically, the smaller members include round steel bars with roughened surfaces, often called “reinforcing steel,” “reinforcing bar,” or “rebar.” Reinforced concrete structures are available commercially in many shapes and sizes, such as slabs, beams, footings, and flat foundations.
Unfortunately, in some concrete structures shear forces can be concentrated, and a condition called “diagonal tension” is created. When a flat concrete slab (such as a concrete floor slab) is suspended and supported by columns (usually of concrete), the weight of the slab and the load that the slab supports are transferred to the columns through relatively small zones of concrete surrounding the columns. Each of these zones is subject to (i) vertical shear forces resulting from the weight and load of the slab and (ii) internal horizontal shear stress resulting from high bending moments in that area. The combination of high vertical shear stress and high horizontal shear stress creates diagonal tension stress in areas around the columns. Diagonal tension stress is problematic because concrete is particularly weak in tension and the diagonal orientation of potential crack zones makes it difficult for typical rebar installation patterns to work effectively. Also, the relatively thin vertical dimension of the concrete slab can limit the length of rebar that can be used, further reducing its effectiveness.
For this reason, supported concrete structures are typically reinforced in the areas around columns or other supporting structures using short smooth vertical steel studs to provide reinforcement. This is done to prevent tensile failure, crack propagation, and consequent structural collapse. However, conventional approaches often provide reinforcement that helps restrain or minimize cracking or breaking only after the cracking or breaking has been initiated. These conventional approaches are typically unable to prevent cracking or breaking from occurring in the first instance. As a result, the concrete and steel studs generally operate sequentially rather than together. That is, the concrete carries much of the load until cracks occur, at which point significantly all of the load is transferred to the steel studs in the cracked area(s) of the concrete.